U.S. authorities banned nearly all 'crop dusting', or aerial spraying of crops, in the United States on Sunday following concerns about a potential terrorist threat. Employees of one Florida crop dusting company say they believe a key suspect in the September 11 terror attacks had been to their office to ask about the possible use of the planes.

J.D. Lee manages the South Florida Crop Care company in Palm Beach County north of Miami. He says the man authorities have identified as Mohamed Atta, the suspect believed to have flown one of the two jetliners into the World Trade Center, twice visited his company, accompanied by several other men. "I did talk to them a few times. Every time they came they would ask the same questions. And one of the gentlemen that works here picked out one of [the suspects] that he recognized and said he had been here twice," said Mr. Lee.

Mr. Lee contacted the FBI last week after he and his employees saw pictures of Mohamed Atta on television. Mr. Lee says the suspect and the men who accompanied him repeatedly inquired about learning to fly crop dusting planes. He says the questions struck him as odd at the time, but not sinister - until the terrorist attacks. "They would come and ask questions about airplanes and stuff," he said. "They indicated they were students, foreign students in this country learning how to fly so they could go home and get a job. They asked how hard these airplanes are to fly, and I told them that these airplanes are very difficult to fly and that you need to be a pretty experienced pilot to fly these airplanes."

Crop dusting planes are typically small, propeller aircraft with a large tank under the fuselage for carrying pesticides and fertilizers that can be dispersed over a wide region.

Revelations of the alleged terrorists' interest in the aircraft led federal aviation authorities to ground virtually all crop dusters Sunday. Federal authorities are not commenting on the possible motives of the hijackers regarding crop dusting. But Florida health officials say the incident has prompted them to review their emergency plans in the event of chemical or biological attack.

J.D. Lee says the ban on crop dusting has virtually shut down his business and that of other crop dusting companies across the country.